What organism are they talking about here that is considered a key species for thousands of other species to survive? algae fish coral

## Step 1
The question is asking about a key species that is essential for the survival of thousands of other species. The options provided are algae, fish, and coral.

## Step 2
Algae are a type of organism that can be found in various environments, including water and soil. They are important for photosynthesis, which is the process by which plants produce oxygen. However, algae are not typically considered a key species for the survival of thousands of other species.

## Step 3
Fish are a type of aquatic animal that are important for the food chain and the ecosystem. However, they are not typically considered a key species for the survival of thousands of other species.

## Step 4
Coral, on the other hand, is a type of marine organism that forms coral reefs. These reefs are home to a vast number of species, providing food, shelter, and breeding grounds. Therefore, coral is considered a key species for the survival of thousands of other species.